1. Field of the Invention
The present invention relates to a process for sulfiding a catalyst containing an S (sulfur)-containing organic additive, in particular a hydrotreating catalyst containing an S-containing organic additive.
2. Prior Art
Hydrotreating catalysts comprise hydrogenation metal components, generally a Group VI metal component such as molybdenum and/or tungsten and a Group VIII metal component, such as nickel and/or cobalt generally on an oxidic carrier. Before use, the hydrogenation metal components present in hydrotreating catalysts will generally be converted into their sulfides. This process is conventionally indicated as sulfidation or presulfidation. It is generally done before the catalyst is used in hydrotreating to ensure a stable reactor performance.
Hydrotreating catalysts containing S-containing organic additives are known in the art. The addition of the S-containing organic additive is often intended to preclude the necessity of a separate presulfiding step.
For example, European patent application 0 300 629 and European patent application No. 0 357 295 describe hydrotreating catalysts comprising a support impregnated with at least one member of molybdenum, tungsten, and/or Group VIII of the Periodic Table, and a mercapto-compound selected from mercaptocarboxylic acids, amino-substituted mercaptanes, di-mercaptanes, and thioacids. The S-containing additive is incorporated into the catalyst composition to obviate the necessity of presulfiding, or at least make the presulfiding less difficult. In particular, the S-containing additive is incorporated into the catalyst to obviate the necessity of dedicating the initial part of the reactor start-up to providing the catalyst with the amount of sulfur needed to attain equilibrium with the reaction environment, or to shorten the time necessary for doing so. Additionally, the necessity of spiking the feed with a sulfur-containing compound such as DMDS is lessened or obviated. Further, since all catalyst particles already contain S when they enter the unit, the homogeneity of the sulfided product will be improved.
European patent application No. 0 506 206 also describes a hydrotreating catalyst comprising an S-containing additive selected from the group of bi-mercaptanes, aminosubstituted mercaptanes, and thiocarboxylic acids. The S-containing catalyst is again intended to avoid the necessity of presulfiding. Some of the catalysts described in this reference are activated by a treatment with hydrogen at a temperature from room temperature up to 400xc2x0 C., preferably 100-300xc2x0 C.
Similar subject-matter is described in European patent application No. 0 338 788, and European patent application No. 0 289 211.
U.S. Pat. No. 5,139,990 describes a hydrotreating catalyst comprising a carrier and hydrogenation metal components which is treated with an aqueous medium comprising a water-soluble or water-miscible S-containing organic additive, followed by drying the resulting catalyst and activating it with hydrogen at a temperature of 100-600xc2x0 C.
U.S. Pat. No. 4,636,487 describes a hydrotreating catalyst comprising a support and a hydroxymercaptide of one or more metals, which may be the reaction product of a mercaptoalcohol and one or more metal compounds. The catalyst may be activated with hydrogen at a temperature of 66-316xc2x0 C.
European patent application No.0 496 592 describes a hydrotreating catalyst comprising a carboxylic acid and an organic sulfur compound which may be a mercaptocarboxylic acid. The amount of organic sulfur compound is so low that the catalyst still needs to be presulfided. No information is given as to how this presulfidation step should be carried out.
U.S. Pat. No. 5,045,518 describes a process in which a conventional hydrotreating catalyst is subjected to ex situ presulfiding followed by in situ presulfiding. Ex situ presulfiding is carried out by contacting the catalyst with a sulfur compound, e.g., by impregnation. The amount is 0.5-1.5 times the stochiometric amount. The sulfur compound may be present in a solvent, which may be water or an organic solvent, which may, e.g., be a gasoline fraction. The use of water-soluble sulfur compounds is preferred. After the impregnation there is a drying step to remove the solvent. The in situ sulfidation may be gas phase or liquid phase, with liquid phase being preferred.
U.S. Pat. No. 5,001,101 describes the preparation of a catalyst by incorporating metals into an alumina hydrogel, followed by shaping, drying, and calcination to prepare a catalyst. The catalyst is subsequently sulfided by a conventional sulfidation procedure, followed by activation at a temperature of at least 900xc2x0 F. (482xc2x0 C.). Conventional sulfidation procedures may include two-step sulfidation processes (col. 7, lines 55-62).
Although the activity of the catalysts containing an S-containing organic additive described in the above references is good, there still is room for improvement. Additionally, it has appeared that when the catalysts of the above references are brought into the hydrotreating unit, undesirable components such as acetic acid may be formed during the start-up. Additionally it was found that the start-up procedure is rather critical to obtain good results.
In one embodiment, our invention is a sulfidation process in which a catalyst composition comprising at least one hydrogenation metal component of Group VI and/or Group VIII of the Periodic Table, and an S-containing organic additive is contacted in two steps with hydrogen and a sulfur-containing compound in the gaseous phase, with the first step being performed at a temperature which is lower than that of the second step.
In a second embodiment, our invention is a catalyst obtained by the above process.
In a third embodiment, our invention is a process for hydrotreating a hydrocarbon feed by contacting the feed with the above catalyst at hydrotreating conditions.
Other embodiments of our invention encompass details about reactant compositions, process steps and conditions, etc., all of which are hereinafter disclosed in the following discussion of each of the facets of our invention.
The Sulfidation Process
It appears that catalysts with a higher activity may be obtained if the catalysts containing an S-containing organic additive are sulfided by way of the process of our invention.
In the process according to our invention, the catalyst is contacted in two steps with hydrogen and a sulfur-containing compound in the gaseous phase, with the first step being performed at a temperature which is lower than that of the second step.
The sulfur-containing compound is H2S and/or a compound which is decomposable into hydrogen sulphide under the conditions prevailing during the contacting of the catalyst with hydrogen and a sulfur-containing compound. Examples of suitable components decomposable into H2S are mercaptanes, CS2, thiophenes, dimethyl sulphide (DMS), dimethyl disulphide (DMDS), and suitable S-containing refinery outlet gasses. The use of H2S alone is preferred. The skilled person knows how to select a sulfur compound which will decompose under the conditions applied.
The total amount of sulfur-containing compound which is incorporated into the catalyst in the process according to the invention, including the amount of sulfur added by way of the S-containing additive is generally selected to correspond to about 50-300%, preferably about 70-200%, more preferably about 80-150%, of the stoichiometric sulfur quantity necessary to convert the hydrogenation metals into Co9S8, MoS2, WS2, and Ni3S2, respectively.
The concentration of sulfur-containing compound in the mixture of H2 and sulfur-containing compound is generally selected to be between about 1 and about 99 wt. %, preferably between about 10 and about 80%, calculated as H2S on the total of H2S and hydrogen. Of course, lower sulfur concentrations in this mixture will either lengthen the duration of the process or increase the required space velocity. The application of gas recycle may be attractive.
In the two-step presulfiding process according to the invention, the first step is generally carried out at a temperature of about 100-250xc2x0 C., preferably about 150-225xc2x0 C. The second step is generally carried out at a temperature of about 150-450xc2x0 C., preferably about 200-400xc2x0 C., more preferably about 225-400xc2x0 C. The gaseous mixtures of H2 and sulfur-containing compound applied in the two steps may be the same or different. If so desired, this process may also be carried out in more than two steps, e.g., in three steps or in a continuous mode, as long as the first step, or the start of the process, is carried out at a lower temperature than a further step, or later part of the process.
The total pressure during the process according to the invention is not critical. It will generally be between atmospheric pressure and about 300 bar, depending on where the process is carried out. If the process is carried out ex situ, the pressure may, e.g., be between atmospheric pressure and about 10 bar. If the process is carried out in situ, the pressure may be much higher, e.g., in the range of about 25 to about 300 bar.
The contacting in the gaseous phase with hydrogen and a sulfur-containing compound can be carried out in any suitable manner, including in fixed bed processes and moving bed processes. Since the sulfiding step may be exothermic by nature, it is important that the temperature of the catalyst is well-controlled. Generally, such control is easier in a moving bed process. In the context of the present specification, a moving bed process is intended to encompass all processes in which the catalyst moves relative to the reactor. Examples are ebullated bed processes and processes carried out in a rotary furnace. In the latter, the contacting can be done either co-currently or counter-currently, with counter-current operation being preferred.
The amount of sulfur incorporated into the catalyst with the S-containing compound in the gas phase will generally be between about 5 and about 95% of the stoichiometric sulfur quantity necessary to convert the hydrogenation metals into Co9S8, MoS2, WS2, and Ni3S2, respectively. It is noted that the amount of S-containing compound with which the catalyst is contacted in the gaseous phase will be much higher than the above-mentioned stoichiometric amount, but not all sulfur will be incorporated into the catalyst.
It is also noted that the S-containing compound present in the gas phase does not refer to decomposition products from the S-containing additive already present in the catalyst but refers to S-containing compound added extraneously to the hydrogen.
The process according to the invention can be carried out ex situ or in situ. In the context of the present specification, the term in situ means in the reactor in which the catalyst will eventually be applied to effect hydrotreating. Conversely, ex situ means outside said reactor. It is preferred to carry out the process according to the invention ex situ, because this generates less downtime for the hydrotreating reactor and simplifies the reactor start-up. Additionally, in ex situ operation, any less desirable side products formed by the decomposition of the S-containing additive will not be formed in the hydrotreating unit. The sulfidation unit may often be better equipped to handle undesirable gases.
If the process according to the invention is carried out ex situ, it may be desirable to passivate the sulfided catalyst prepared in this way, since sulfided catalysts may be self-heating. Passivation can be done by contacting the sulfided catalyst with an oxygen-containing compound under controlled conditions. The use of an oxygen-containing gas, such as air, is a well-known embodiment. Alternatively, the sulfided catalyst may be passivated by being contacted with an organic liquid, such as diesel, gas oil, white spirit, or lube oil. Passivation processes are known in the art. See, for example, EP-897 748 and NL 8900914, which describe the use of hydrocarbons, and V. M. Browne, S. P. A. Louwers, and R. Prins, Catalysis Today volume 10 number 3 pp 345-352 (1991) and S. P. A. Louwers, M. W. J. Craje, C. Geantet, A. M. van der Kraan, and R. Prins, Journal of Catalysis volume 144 number 2 pp. 579-596 (1993), both of which describe the use of oxygen.
The Additive-containing Catalyst
In principle, the additive-containing catalyst can be any catalyst which comprises a Group VIB hydrogenation metal and/or a Group VIII hydrogenation metal, and an S-containing organic additive, generally on a carrier. Catalysts comprising the combination of a Group VIB hydrogenation metal and a Group VIII hydrogenation metal are preferred. As will be evident to the skilled person, the metals may be present in any form. When they are incorporated into the catalyst composition they are often in the form of their salts or oxides. After calcination they are converted partly or wholly into their respective oxides. After sulfidation and during use the metals are at least partly present in the sulfidic form.
As Group VIB metals may be mentioned molybdenum, tungsten, and chromium. Group VIII metals include nickel, cobalt, and iron. Catalysts comprising molybdenum and/or tungsten as Group VIB metal component and nickel and/or cobalt as Group VIII metal component are the most common. The catalyst usually has a metal content in the range of 0.1 to 50 wt. % calculated as oxides on the dry weight of the catalyst not containing the additive. The Group VIB metal will frequently be present in an amount of 5-40 wt. %, preferably 15-30 wt. %, calculated as trioxide. The Group VIII metal will frequently be present in an amount of 1-10 wt. %, preferably 2-7 wt. %, calculated as monoxide. The catalyst may also contain other components, such as phosphorus, halogens, and boron. Particularly, the presence of phosphorus in an amount of 1-10 wt. %, calculated as P2O5, may be preferred.
The catalyst carrier may comprise the conventional oxides, e.g., alumina, silica, silica-alumina, alumina with silica-alumina dispersed therein, silica-coated alumina, magnesia, zirconia, boria, and titania, as well as mixtures of these oxides. As a rule, preference is given to the carrier comprising alumina, silica-alumina, alumina with silica-alumina dispersed therein, or silica-coated alumina. Special preference is given to the carrier consisting essentially of alumina or alumina containing up to 25 wt. % of other components, preferably silica. A carrier comprising a transition alumina, for example an eta, theta, or gamma alumina is preferred within this group, with a gamma-alumina carrier being especially preferred. Additionally, although at present less preferred, the catalyst may contain 0-60 wt. % of zeolite.
The catalyst""s pore volume (measured via N2 adsorption) generally is in the range of 0.25 to 1 ml/g. The specific surface area will generally be in the range of 50 to 400 m2/g (measured using the BET method). Generally, the catalyst will have a median pore diameter in the range of 7-20 nm, as determined by N2 adsorption. The figures for the pore size distribution and the surface area given above are determined after calcination of the catalyst at 500xc2x0 C. for one hour.
The catalyst is suitably in the form of spheres, pellets, beads, or extrudates. Examples of suitable types of extrudates have been disclosed in the literature (see, int. al., U.S. Pat. No. 4,028,227). Highly suitable are cylindrical particles (which may be hollow or not) as well as symmetrical and asymmetrical polylobed particles (2, 3 or 4 lobes).
The additive present in the catalyst may be any S-containing organic additive. In the context of the present specification the term organic additive refers to an additive comprising at least one carbon atom and at least one hydrogen atom.
Preferred compounds include organic compounds having at least one mercapto-group. Within the group of mercapto-compounds, mercaptocarboxylic acids represented by the general formula HSxe2x80x94R1-COOR, wherein R1 stands for a divalent hydrocarbon group with 1xe2x80x94 about 10 carbon atoms and R stands for a hydrogen atom, an alkali metal, an alkaline earth metal, ammonium, or a linear or branched alkylgroup having 1 to about 10 carbon atoms. Examples include mercaptoacetic acid (HSxe2x80x94CH2-COOH), beta-mercaptoprioprionic acid (HSxe2x80x94CH2CH2-COOH), methylmercaptoacetate (HSxe2x80x94CH2-COOCH3), ethyl 2-mercaptoacetate (HSxe2x80x94CH2-COOC2H5), ethylhexyl mercaptoacetate (HSxe2x80x94CH2-COOC8H17), and methyl 3-mercaptoproprionate ((HSxe2x80x94CH2CH2-COOCH3). Further compounds preferred within the group of mercapto-compounds include aminosubstituted mercaptanes represented by the general formula H2Nxe2x80x94R2-SH, wherein R2 stands for a divalent hydrocarbon group having 1xe2x80x94 about 15 carbon atoms. Examples of these compounds include 2-amino ethanethiol (H2Nxe2x80x94CH2CH2-SH), and 4-amino thiophenol (H2Nxe2x80x94C6H4-SH).
Additional compounds within the group of mercapto-compounds are the di-mercaptanes represented by the general formula HSxe2x80x94R3-SH, wherein R3 stands for a divalent hydrocarbon group having 1xe2x80x94 about 15 carbon atoms. Examples of these compounds include ethanedithiol (HSxe2x80x94CH2CH2-SH) and 1,4-butanedithiol (HSxe2x80x94(CH2)4-SH).
Preferred compounds also include thioacids of the formula R4-COSH, wherein R4 stands for a monovalent hydrocarbon group having 1xe2x80x94 about 15 carbon atoms. Examples of these compounds include thioacetic acid (CH3-COSH) and thiobenzoic acid (C6H5COSH). Dithioacids of the formula HSOCxe2x80x94R5-COSH, wherein R5 is a divalent hydrocarbon group with 1xe2x80x94 about 15 carbon atoms may also be suitable. An example is dithioadipic acid (HSOCxe2x80x94C4H10-COSH).
Preferred compounds also include mercaptoalcohols of the general formula R6Sxe2x80x94R5-(OH)n, wherein R5 represents an alkyl group having from 1 to about 15 carbon atoms or a phenyl group, R6 represents a hydrogen atom or an alkyl group having 1 or 2 carbon atoms, and n is 1 or 2. Examples of these compounds include 2-mercaptoethanol, 2-(methylthio)ethanol, 2-(ethylthio)ethanol, 3-mercapto-2-butanol, 4-mercaptophenol, 2-(methylthio)phenol, 4-(methylthio)phenol, 2-(ethylthio)phenol, 3-mercapto-1,2,-propanediol, 3-methylthio-1,2, propanediol, and 3-ethylthio-1,2, propanediol. Other suitable compounds include sulphoxides of the formula R7-SOxe2x80x94R8, wherein R7 and R8 are hydrocarbon groups with 1-5 carbon atoms. An example is dimethyl sulfoxide (CH3-SOxe2x80x94CH3).
Ammonium thiocyanate and thiourea may also be useful compounds, as may be the various dithiocarbamic acids and the salts thereof, such as ethylene bisdithiocarbamic acid and its salts, and dimethyl dithiocarbamic acid and its salts. Other suitable compounds include mercaptodiathiazoles and their salts, such as 2,5-dimercapto-1,3,4,-diathiazoles and its salts.
Other compounds which may be useful are polysulfides of the formula R9-Sxxe2x80x94R10, wherein x is a value of 1xe2x80x94 about 15 and R9 and R10 are alkyl groups, preferably branched alkyl groups, with 1xe2x80x94 about 30 carbon atoms. Related compounds are those with the formula HOxe2x80x94R11-Sxxe2x80x94R12-OH, wherein x is a value of 1-15 and R11 and R12 are alkyl groups with 1 xe2x80x94 about 8 carbon atoms.
At this point in time the mercapto-compounds, in particular the mercaptocarboxylic acids are considered preferred for reasons of catalyst activity. Other compounds, in particularly those which are soluble in or miscible with water may be preferred for environmental reasons (less smell and no organic solvent necessary).
A single compound as well as a combination of compounds may be used as additive.
The amount of additive present in the additive-containing catalyst depends on the specific situation. It was found that the appropriate amount of additive generally lies in the range of about 0.01-2.5 moles of additive per mole of hydrogenation metals present in the catalyst. If the amount of additive added is too low, the advantageous effect associated with its presence will not be obtained. On the other hand, the presence of an exceptionally large amount of additive will not improve its effect. Generally it is intended that the amount of sulfur incorporated into the catalyst by way of the additive is selected to correspond to about 5-200%, preferably about 50-200%, more preferably about 80-150%, of the stoichiometric sulfur quantity necessary to convert the hydrogenation metals into Co9S8, MoS2, WS2, and Ni3S2, respectively.
The way in which the additive is incorporated into the catalyst composition is not critical to the process according to the invention. The additive may be incorporated into the catalyst composition prior to, subsequent to, or simultaneously with the incorporation of the hydrogenation metal components. For example, the additive can be incorporated into the catalyst composition prior to the hydrogenation metal components by being added to the carrier before the hydrogenation metal components are. This can be done by mixing the additive with the carrier material before it is shaped, or by impregnating the shaped carrier material with the additive. This embodiment is not preferred at this point in time.
Alternatively, the additive can be incorporated into the catalyst composition simultaneously with the hydrogenation metal components. This can be done, e.g., by mixing the additive and the hydrogenation metal components with the carrier material before shaping or by impregnating the carrier with an impregnation solution comprising the hydrogenation metal components and the additive, followed by drying under such conditions that at least part of the additive is maintained in the catalyst.
It is also possible to incorporate the additive into the catalyst composition subsequent to the hydrogenation metal components. This can be done, e.g., by first incorporating the hydrogenation metal components into the catalyst composition, e.g., by mixing them with the carrier material or by impregnating the carrier with them, optionally followed by drying and/or calcining, and subsequently incorporating the additive, e.g., by impregnation, optionally followed by drying under such conditions that at least part of the additive is maintained in the catalyst.
Depending on the nature of the additive and the way in which it is incorporated into the catalyst composition, the additive may be used in solid form, in liquid form, or dissolved in a suitable solvent. It may be preferred for the additive to be incorporated into the catalyst dissolved in water.
Use of the Sulfided Catalyst Prepared According to the Invention
The catalyst sulfided by the process according to the invention can be used in the hydrotreating of hydrocarbon feeds. The hydrotreating generally takes place under conventional hydrotreating conditions, such as temperatures in the range of about 250-450xc2x0 C., pressures in the range of about 5-250 bar, space velocities in the range of about 0,1-10 hxe2x88x921, and H2/oil ratios in the range of about 50-2000 Nl/l. Examples of suitable feeds include middle distillates, kerosine, naphtha, vacuum gas oils, heavy gas oils and residues. Preferably, the hydrocarbon feed contains at least about 0.2 wt % of sulfur, calculated as atomic sulfur S. Examples of suitable hydrotreating reactions are (deep) hydrodesulfurisation, hydrodenitrogenation, hydrodearomatisation, and hydrodemetallisation. (Deep) hydrodesulfurisation, hydrodenitrogenation, and hydrodearomatisation are preferred.